Field of the Invention
The present invention relates to a solid-state imaging device, and more particularly relates to a solid-state imaging device suitable for an imaging apparatus such as a digital camera.
Description of the Related Art
There is increased demand for wider dynamic ranges in images acquired by imaging apparatuses such as digital cameras. Japanese Patent Laid-Open No. 2004-363193 proposes a technology to deal with this issue by differentiating the aperture area of multiple photoelectric conversion portions within a pixel from each other, changing the ratio of the amount of light entering the photoelectric conversion portions, thereby acquiring the types of pixel signals; high-sensitivity signals and low-sensitivity signals. These are then synthesized, widening the dynamic range.
There is also increased demand for realization of an imaging apparatus that can acquire still image signals while acquiring moving image signals. Generally, in order to obtain smooth moving images, shooting is preferably performed at an exposure time (charge accumulation period) around the same as the readout frame rate of the solid-state imaging device. On the other hand, the exposure time in the case of still images is preferably set according to the motion speed of the subject. Accordingly, acquiring still image signals while acquiring moving image signals necessitates acquisition of two image signals that each have different exposure times.
Japanese Patent Laid-Open No. 2004-120391 discloses a solid-state imaging device that has multiple photoelectric conversion elements (equivalent to the photoelectric conversion portions in Japanese Patent Laid-Open No. 2004-363193) having different exposure times in a single pixel, to acquire still image signals while acquiring moving image signals. The area of the photoelectric conversion element having a relatively short exposure time is relatively wide, while the area of the photoelectric conversion element having a relatively long exposure time is relatively small, and the sensitivity differs between the photoelectric conversion element for moving images and the photoelectric conversion element for still images. Note that “sensitivity of [the] photoelectric conversion element (photoelectric conversion portion)” is defined as the proportion of the amount of electric charges accumulated in the photoelectric conversion portion as to the amount of light entering the pixel per unit of time.
Japanese Patent Laid-Open No. 2002-314062 discloses a solid-state imaging device that has distance-measuring pixels (hereinafter referred to as “ranging pixels”) having ranging functions to detect the distance to a subject by phase-difference measurement, as conventional art. A ranging pixel is provided with multiple photoelectric conversion portions, and is configured such that light beams which have passed through different regions of the pupil of the photographing lens are each guided to different photoelectric conversion portions. Images of light beams, which have each passed through the pupil region shifted away from the optical axis of the photographing lens to opposite sides from each other (hereinafter referred to as “ranging image”) are generated from the signals acquired by each of the multiple photoelectric conversion portions provided to each ranging pixel. The distance to the subject can then be detected using the principle of triangulation, based on the amount of misalignment between the ranging images generated from each of the light beams that have passed through different pupil regions of the photographing lens. When imaging, the outputs of signals acquired at the multiple photoelectric conversion portions within the pixel are added and acquired, thereby yielding imaging signals.
Now, when acquiring ranging images while acquiring images of different sensitivities the following problem occurs. In order to acquire one of multiple imaging signals having different sensitivities while acquiring another, using the techniques disclosed in Japanese Patent Laid-Open Nos. 2004-363193 and 2004-120391, the amount of light entering each of the multiple photoelectric conversion portions provided within the pixel needs to be changed. Specifically, a configuration is employed where two photoelectric conversion portions are provided in the pixel, and the optical axis of the microlens is shifted away from the center of a barrier region for separating the two photoelectric conversion portions. However, this layout results in a shorter distance (baseline length) between pupil regions of the photographing lens through which the light beams received by the photoelectric conversion portions pass, and the precision of ranging deteriorates.
On the other hand, in a case where the optical axes of microlenses passes through the center of a barrier region for separating the two photoelectric conversion portions, as in the case of Japanese Patent Laid-Open No. 2002-314062, the distance (baseline length) between pupil regions of the photographing lens through which the light beams received by the photoelectric conversion portions pass is longer, so the precision of ranging improves. However, the amounts of light entering the two photoelectric conversion portions through the microlens are approximately the same, so acquiring one of multiple imaging signals having different sensitivities while acquiring another becomes difficult.
It has been found desirable to enable ranging signals (signals for acquiring ranging images) to be acquired while acquiring imaging signals (signals for acquiring images) having different sensitivities from each other, and also preventing ranging precision from deteriorating.